Mr. Hitachiin is the father of Hikaru and Kaoru. He's a supporting character who only appears in the manga. He works for a computer software developer and is married to the twins' mother, Yuzuha Hitachiin, a successful fashion designer. His first name is unknown and he took his wife's surname upon marriage for unspecified reasons. He is seen to be a level-headed and loving father who can always tell the difference between his sons. On a personal level, however, he has a weak presence and is easily overlooked by people. During their first meeting, Haruhi assumes him to be a sort of ninja because despite being around them the whole day, he isn't noticed at all.
- (To Haruhi, Chapter 45) So, Fujioka-san, you can distinguish them. For a long time, me and my wife were busy... It resulted in these two developing lonely feelings. Because of that, from their normal brother's mutual affection they became highly dependent on each other. Their desire of being recognized is strong. They isolated themselves from the others because they were afraid, these two children.